Lift truck load lifting mechanism

ABSTRACT

A load lifting mechanism for lift trucks in which an extensible mast carries a cantilever type load lifting carriage and is vertically actuated by a hydraulic ram and associated load lifting chains. The bending moment created by the load carried on the carriage is counterbalanced by a bending moment derived from load lifting tension elements acting on counterbalancing arms attached to an upper section of the mast, thereby substantially reducing or eliminating bending stresses on the mast regardless of the size of the load being lifted. A pair of laterally spaced chains are utilized as the tension elements in conjunction with laterally spaced counterbalancing arms and similarly spaced chain orienting arms connected to a lower section of the mast and/or to truck anchor points so that lateral as well as fore and aft stability of the mast and associated lift truck is increased. Preferably, the mast is oriented in a fixed upright position relative to the lift truck and a tilting carriage as disclosed herein is used for tilting the forks or other load lifting device attached to the carriage. Several embodiments of counterbalanced masts and telescoping dual rail mast sections and lift chain reeving arrangements are also disclosed.

United States Patent 91 Ramsey [451 Apr. 17, 1973 LIFT TRUCK LOAD LIFIING MECHANISM [75] Inventor: Keith E. Ramsey, Jackson, Mich.

[73] Assignee: The Knickerbocker Company, Jackson, Mich.

[22] Filed: Jan. 5, 1971 [21] App]. No.:'104 ,118

Related U.S. Application Data [63] Continuation of Ser. No. 660,630, Aug. 15, 1967,

abandoned.

[52] U.S. Cl. ..214/70l P, 187/9, 187/94 [51] Int. Cl. ..B66f 9/16 [58] Field of Search ..2l4/660, 670, 671, 214/672, 673, 674, 700, 701 P; 187/94, 9

[56] References Cited UNITED STATES PATENTS 3,051,265 8/1962 Boyajian et al .187/9 1,875,103 8/1932 Mosel ..2l4/70l P Primary ExaminerGerald M. Forlenza Assistant Examiner-Lawrence J. Oresky Attorney-Barnes, Kisselli, Raisch & Choate [57] ABSTRACT A load lifting mechanism for lift trucks in whichan extensible mast carries a cantilever type load lifting carriage and is vertically actuated by a hydraulic ram and associated load lifting chains. The bending moment created by the load carried on the carriage is counterbalanced by a bending moment derived from load lifting tension elements acting on counterbalancing arms attached to an upper section of the mast, thereby substantially reducing or eliminating bending stresses on the mast regardless of the size of the load being lifted. A pair of laterally spaced chains are utilized as the tension elements in conjunction with laterally spaced counterbalancing arms and similarly spaced chain orienting arms connected to a lower section of the mast and/or to truck anchor points so that lateral as well as fore and aft stability of the mast and associated lift truck is increased. Preferably, the mast is oriented in a fixed upright position relative ,to the lift truck and a tilting carriage as disclosed herein is used for tilting the forks or other load lifting device attached to the carriage. Several embodiments of counterbalanced masts and telescoping dual rail mast sections and lift chain reeving arrangements are also disclosed.

23 Claims, 28 Drawing Figures PAIENIEM 1 7 sum 01 0F 17 |NVENTOR KIETH E- RAMSEY ATTORNEYS PATENTEUAPR 1 71975 SHEET 02 0f 17 Y my WW p FL H T U W N L wmu I U 5 m 7 Y 7 B 7| 4 6 4 v 2 /G /I W? V 4 3 ATTORNEYS FULL LIFT PATENTEBAPR I 71975 sum 03 or 17 DMPUJQPUK *JMPMJQEOU PHI) mmuh JJQH INVENTOR TILLV N% KIETH E. RAMSEY m mtfi,

ATTORNEYS PA TENTED APR 1 H975 sum INVENTOR KEITH E. RAMSEY OVERHEAD CLEARANCE ATTORNEYS PATENTEBAPR 1 Y W 3.721781 SHEET us or 17 INVENTOR KIETH E. RAMSEY o 0 o n 00 FIG. 8

BY 162M,

e a u o o 0 O a 0 a go no ll lul lzlll ATTORNEYS PATENTEUAPR 1 H975 SHEET 08 0F 17 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTEDAPR 1 Tim 3; 727, 7831 saw 07 0F 17 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTEDAPR 1 1 I913 '3', 727; 781

SHEET 08 HF 17 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTEI] APR 1 71975 sum 09 0F 17 PATENTEU APR n 1915 sum 10 0F 17 FIG. 17

INVENTOR KEITH E. RAMSEY ATTORNEYS PATENTED APR 1 7 I973 SHEET 11 0F 17 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTED APR 1 7 i975 sum 12 0F 17 INVENTOR KEITH E. RAMSEY ATTORNEYS PATENTEBAPR I 71975 sum 13 or 1 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTEBAPR I 71975 SHEET 1n HF 17 INVENTOR KIETH EA RAMSEY WMv-M I BY ATTORNEYS PATENTEU APR 1 7 I975 SHEET INVENTOR KEITH E. RAMSEY W W am;

ATTORNEYS PATENTEDAPR 1 H915 3. 727. 781

sum 15 or 17 INVENTOR KIETH E. RAMSEY ATTORNEYS PATENTEDAPR 1 H973 sum 17 0F 1? INVENTOR KIETH E. RAMSEY ATTORNEYS LIFT TRUCK LOAD LIFTING MECHANISM This application is a. continuation of my copending parent application Ser. No. 660,630, filed Aug. 15, 1967 and titled Lift Truck Load Lifting Mechanism, now abandoned in favor of this continuation application.

An object of the present invention is to provide an improved load lifting mechanism for industrial and/or off-the-road lift trucks of the type having an extensible load lifting mast and associated load lifting chains actuated by a hydraulic ram to lift a load supported in cantile'ver fashion on a carriage of the mast wherein loadinduced bending stresses are counterbalanced by forces transmitted in tension through the load lifting chains to thereby-provide, in conjunction with other features of the invention, a load lifting mechanism which results in: (l) an'economical and lightweight construction which is efficient and reliable in operation, (2) less strain on the mast parts and truck frame and axle, (3) an increased load lifting capacity, (4) greater stability, (5) lower center of gravity, (6) less power to raise the load, (7) faster lift speed, (8) a smaller oil reservoir in the hydraulic supply system, (9) adaptability to a variety of existing truck designs, (10) a greater range of load lifting capacities for a given design of truck and mast, (11) greater off-center load ratings both fore and aft and side to side, (12) a greater margin of safety to the operator as well as the equipment and l3) improved visibility.

Another object is to provide an improved tilting carriage mechanism for lift truck masts which pivots the load carried on the carriage substantially about the center of gravity of the load, thereby reducing the power required to actuate the tilting carriage, and which minimizes the space and structural requirements of the carriage.

A further object is to provide an improved lift truck equipped with a counterbalanced load lifting mechanism of the aforementioned character which cooperates with an overhead guard for the operator of the truck to provide improved protection for the operator and better support for the mast while reducing the stresses imposed by the mast on the truck frame.

Other objects as well as the features and advantages of the present invention will become apparent from the following detailed description taken in conjunction with the accompanying drawings wherein:

FIG. 1 is a side elevational view of an extensible load lifting mechanism and lift truck constructed in ac cordance with the present invention with the carriage and mast thereof shown in full lift position.

FIGS. 2, 3, 4, and 5 are simplified semi-schematic vertical center sectional views respectively showing the mast of FIG. 1 in fully extended position (FIG. 2), about half-way extended (FIG. 3), slightly extended with the carriage at the upper limit of the free lift range of the mast (FIG. 4), and with the mast fully collapsed and the carriage at ground level (FIG. 5).

FIG. 6 is a fragmentary side elevational view of the mast structure of F IG. 1 with the mast in its fully collapsed condition corresponding to FIG. 5.

FIG. 7 is a fragmentary vertical section taken on the line 7-7 ofFIG. 6.

FIG. 8 is a fragmentary side elevational view of the mast of FIG .-l shown in the position of FIG. 3 and with portions broken away to illustrate detail.

FIG. 9 is a top plan view of the mast of FIG. 1.

FIG. 10 is a horizontal section taken on the line 10 10 of FIG. 1.

FIG. 11 is a fragmentary side elevational view of the mast of FIG. 1 with the ram and mast sections shown in telescoped collapsed condition of FIG. 5 but with the carriage and counterbalancing arms removed for clarity.

FIG. 12 is a fragmentary horizontal section taken on line 1212 of FIG. 11.

FIG. 13 is'the fragmentary side elevational view of the mast of FIG. 1 shown in the partially extended condition of FIG. 4 with the carriage and counterbalancing arms removed and portions broken away to better illustrate detail.

FIG. 14 is a fragmentary vertical center sectional view taken on the line 14-14 of FIG. 9 illustrating on an enlarged'scale the hydraulic ram of the load lifting mechanism in fully extended condition.

FIG. 15 is a vertical sectional view of the ram similar to that of FIG. 14 but showing the ram in its fully collapsed or telescoped condition.

FIGS. 16, 17, and 18 are horizontal sectional views taken respectively on the lines 16-16, 17-17, and 1818 of FIG. 14.

FIG. 19 is a fragmentary front elevational view of the lower portion of the mast in collapsed condition illustrating the load lifting carriage of the invention.

FIG. 20 is a fragmentary side elevational view of the carriage and mast structure shown in FIG. 19 but on a larger scale.

FIG. 21 is a horizOntal section taken on the line 21 21 of FIG. 20.

FIG. 22 is a fragmentary side elevational view of the structure shown in FIG. 20 illustrating by solid lines and in phantom line positions the range of tilting movement of the carriage.

FIG. 23 is a fragmentary perspective semi-schematic view of a second embodiment of a lift mast employing the ramof the first embodiment of FIGS. 122 and a similar chain rigging arrangement applied to a noncounterbalanced four section mast.

FIGS. 24 and 25 are semi-schematic fragmentary perspective view of third and fourth embodiments respectively of extensible lift truck masts in accordance with the present invention.

FIGS. 26, 27, and 28 are semi-schematic side elevational views of the second, third and fourth mast embodiment shown respectively in FIGS. 23, 24, and 25 in their respective full-lift positions.

INTRODUCTION The principles of the present invention are applicable to load lifting mechanisms incorporating an extensible framework, commonly termed a mast, made up of one or more sections, depending upon the load lifting capacity and vertical load lifting range desired. The term mast section" refers usually to a rectangular framework made up generally of a pair of horizontally spaced and vertically extending rails suitably interconnected by horizontal braces and adapted to telescopically interengage with the rails of another such section of the mast. The term rails" refers to the vertical side members of a mast section, which may be millformed beam sections, and which are commonly used in pairs in lift mast constructions as the uprights of a mast section. The term ram as used herein refers to the hydraulically operated piston and cylinder unit employed to impart vertical movement to the load lifting mechanism, and preferably comprises a simple twopart ram made up of a cylinder which constitutes the external member of the ram and an internal plunger which telescopes within the cylinder. However, other known multi-part ram constructions may be employed if desired, as will become apparent hereinafter. The term carriage refers to the apron which travels vertically on the uppermost section of the mast and the forks or other associated cantilevered attachment which directly carries the cargo or load to be raised, lowered and/or transported. The term chain refers to the usual flexible load supporting elements which transmit tension loading and operatively interconnect the ram, mast sections and carriage. These elements preferably comprise the well known link and roller type chains since they operate with a minimum of friction and stretch, but other types of chains, cables, belts or equivalent elements may be employed if their stretch factor" is suitably taken into account.

FOUR-RAIL CAPACITY MAST 30 The first embodiment of a load lifting mechanism constructed in accordance with the present invention is illustrated inFIGS. l-22 inclusive and comprises a twosection mast 30 having the lifting range of a conventional four-rail" mast. Referring to FIG. 1, mast 30 is shown extended to its full height and mounted in fixed vertical position on a lift truck 32 which may be of the off-the-road type shown or a hard tire industrial type. Despite its high lift range and low collapsed clearance, mast 30 has only two sections, a lower, dual rail section 34 supported near its lower end on the front pin 36 of truck 32, and rigidly connected at its upper end to the rear of truck 32 by an overhead framework 38 which also serves as a safety guard for the operator of the truck. The other, upper section 40 of mast 30 is vertically movea ble and slideably telescopes along the outer sides of section 34 when the two sections overlap in the lower lifting range of the mast. Mast 30 is equipped with a load lifting carriage 42 which tracks on section 40, with a two-part ram 44, and with two sets of lift chains 58, 58' and 62, 62'.

Further details of the structure and operation of mast 30 will become apparent from the detailed description of the mast structure as shown in FIGS. 6-22 inclusive. However, it is believed that prefacing such description with an explanation of the structural organization and operating principles of the principal components of mast 30 as shown semi-schematically in FIGS. 2-5 inclusive will better facilitate an understanding of the invention. In these semi-schematic views section 40 is shown spaced horizontally out in front or forward of section 34 in order to permit clearer illustration of the chain reeving arrangement, it being understood that in practice section 40 embraces section 34 and thus is vertically aligned therewith as shown in FIGS. 1 and 6-13. Also, FIGS. 2-5 inclusive show only the right-hand components (as viewed by the truck operator) of the mast sections and chain rigging. Since much of the mast structure is symmetrical, the left-hand components are generally duplicates of the right-hand components and their reference numerals have been given a prime mark suffix to indicate this relationship.

Referring to FIGS. 2-5 inclusive, carriage 42 has a pair of vertically spaced rollers 46 and 48 linked to an apron 50 of the carriage by a tilting mechanism described hereinafter in conjunction with FIGS. 19-22. Rollers 46, 48 track in the outwardly facing channel or groove 52 defined by the channel-shaped rail 54 of section 40 to thereby guide vertical travel of carriage 42 on section 40 and to provide cantilever support for the apron throughout such travel. A single hydraulic ram 44 is interposed structurally and functionally between sections 34 and 40 to vertically extend mast 30 and to elevate carriage 42 on section 40. Preferably, the lower member of ram 44 is an external cylinder 56 suspended for vertical movement by a first pair of laterally spaced chains 58, 58' from section 34, and the upper member constitutes the ram plunger which is a cylinder-type piston 60 telescopically received in the upper end of cylinder 56. The upper mast section 40 is suspended on plunger 60 by a second pair of laterally spaced chains 62, 62.

A first pair of counterbalancing arms 64, 64' are rigidly fixed to the upper end of section 40 and extend rearwardly therefrom in outwardly diverging relation to one another on the opposite side of the mast from the forwardly extending forks 66 of carriage 42. A second pair of arms 68, 68 are rigidly fixed to the upper end of section 34 and are oriented in the same manner as arms 64, 64. A sheave 70 is rotatably supported by arm 64 at the outer end thereof and another sheave 72 is rotatably supported near the fixed end of arm 64 to guide chain 58 along the vertical path of travel of apron 50. Lower arm 68 also rotatably carries two chain sheaves 74 and 76, sheave 74 being vertically aligned with sheave 70 near the outer end of arm 68 and sheave 76 being mounted near the junction of arm 68 and section 34. A pair of sheaves 78, 78' are journalled on the lower end of ram 44, one on each side of cylinder 56, and another pair of sheaves 80, 80' are journalled on the upper end of plunger 60. Chains 58, 58 are each fixed at one end respectively by connections 86, 86 to the upper end of section 34 and have runs 1 16, 116' extending downwardly therefrom to sheaves 78, 71' respectively, thence are trained around sheaves 78, 78, and have runs 114, 114 extending vertically up to sheaves 76, 76 respectively. Chains 58, 58' then run out to and under sheaves 74, 74', then upwardly in a vertical run 1 12, 1 12' to and over sheaves 70, 70, then horizontally to and over the respective sheaves 72, 72, and finally downwardly in vertical runs 113, 113' to connection 88, 88' with the uprights of apron 50.

The second pair of chains 62, 62' are fixed at one end 82, 82' to the lower end of section 40 and then extend upwardly in vertical runs 63, 63' over sheaves 80, 80 respectively and then downwardly in vertical runs 65, 65' to connections 84, 84 with the upper end of cylinder 56.

Cylinder 56 is guided for vertical movement relative to section 34 by three horizontally spaced rollers 90, 92 and 94 (see also FIG. 10) preferably journalled on the upper end of section 34 at degree angular intervals for rolling engagement with the outer surface of cylinder 56. A pair of guide rollers 96, 96' are rotatably mounted on the lower end of ram-44 below sheaves 78, 78', one on each side of cylinder 56, and respectively track in the inwardly facing channel grooves 98, 98' 

1. A load lifting mechanism for a vehicle comprising an extensible upright mast adapted to be supported at its lower end on the vehicle and including a vertically movable mast section and a hydraulic ram forming a vertical structural support member of said mast extending between the lower end of said mast and said mast section, said mast section being disposed at the upper end of said mast, means operably connecting said ram to said mast section such that said mast section is operably supported by and vertically elevated by actuation of said ram, guide means maintaining said mast section in angular alignment with the lower end of said mast via said ram, a load supporting carriage having cantilever load lifting members extending therefrom for supporting a load with its center of gravity spaced horizontally outwardly from said ram, means supporting said carriage in cantilever relationship on said mast section and vertically movable along said mast section, counterbalancing arm means fixedly mounted on and extending from said mast section in a direction generally opposite to said load lifting members, and flexible tension means operably connected at one end with said ram and at the other end with said carriage for exerting in tension a load lifting force on said carriage to cause vertical load lifting movement of said carriage in response to actuation of said ram, first and second support means mounted on said mast section and said arm means respectively and training said flexible means on said counterbalancing arm means such that said flexible means has a first run extending downwardly from said first support means to a load lifting connection with said carriage and a second run extending downwardly from said second support means at a point on said arm means spaced horizontally a predetermined distance in said opposite direction correlated with the load lifting tension force in said flexible means and connector means for operably connecting said second run to a support point remote from said mast section and fixedly associated with said lower end of said mast or with the vehicle at an elevation below said second support means such that said second run of said flexible means acting on said arm means develops a moment acting on said mast section proportional to and oppositely to the load induced moment exerted via said load lifting members, said carriage and said carriage support means on said mast section so as to substantially counterbalance load induced bending forces acting via said carriage support means on said mast section whereby said bending forces are reacted in said mast section to thereby isolate said ram from said bending forces.
 2. The combination set forth in claim 1 wherein said ram comprises at least a cylinder member and a plunger member telescopically received in said cylinder member, and wherein said guide means comprises key and keyway means disposed radially intermediate said ram members and extending axially thereof in sliding engagement with at least one of said ram members to prevent relative rotation therebetween.
 3. The combination set forth in claim 2 wherein said guide means also includes a crosshead secured to the upper end of the uppermost of said ram members, said crosshead having means engaging said mast section to prevent relative rotation between said ram members and said mast section.
 4. The combination set forth in claim 1 wherein said counterbalance arm means comprises at least two rigid arms each rigidly fixed at one end to said mast section and extending therefrom to a free end spaced said predetermined distance in said opposite direction, said arms being spaced from one another in a direction transverse to said directions in which said load lifting members and said arms extend, said flexible tension means comprising two flexible elements associated one with each of said arms and each having said first and second runs, said second runs and said connector means being oriented relative to said mast to provide counterbalancing forces thereon in response to tilting of said mast traNsversely of said directions in which said load lifting members and said arms extend.
 5. The combination set forth in claim 4 wherein said arms diverge from one another in said opposite direction.
 6. The combination set forth in claim 5 wherein said arms are secured to said mast section in the vicinity of the upper end thereof.
 7. A load lifting mast adapted to be mounted upright on a lift truck comprising an extensible framework including a plurality of mast sections, the lowermost one of said sections being adapted to be mounted on the truck to prevent relative vertical movement therebetween, a second one of said sections being movable up and down relative to the fixed section and constituting the uppermost section of said mast, said second section comprising first and second horizontally spaced upright rails, a carriage movable up and down on said second section, said extensible framework including power means operably connected to said second section for raising and lowering said second section with said carriage thereon, flexible tension means operably connected to said carriage and said second section for lifting said carriage on said second section in response to upward movement of said second section, load supporting means mounted on said carriage for movement therewith and projecting from said framework in one direction, first and second counterbalancing arms fixedly connected to the upper end of said first and second rails respectively and projecting therefrom in a direction opposite to said one direction and being spaced from one another laterally of said mast for applying fore and aft and side tilt balancing moments to said second section, and first and second support means mounted respectively on said first and second arms at a predetermined distance outwardly from said mast in said opposite direction, said support means operably connecting said flexible means to said counterbalancing member, said flexible means having first and second runs extending respectively downwardly from said first and second support means and connector means for operably connecting said first and second runs to associated support points remote from said second mast section and fixedly associated with said framework or the lift truck at an elevation below said first and second support means for applying downward forces via said first and second runs to said arms proportional to the load being supported by said load supporting means so as to counterbalance the load induced bending forces acting via said carriage rails whereby said load induced bending forces and said counterbalancing forces are reacted solely in said second section to thereby relieve the remainder of said mast components from such bending forces.
 8. A load lifting carriage and mast section assembly for use on an extensible upright mast of the type adapted to be supported at its lower end on a vehicle and adapted at its upper end to support said assembly thereon and having an extending mechanism for vertically extending said mast, said assembly comprising a mast section adapted to be mounted on the upper end of said mast so as to be operably supported by and vertically elevated by actuation of said extending mechanism, guide means for maintaining said mast section in angular alignment with the upper end of the mast, a carriage including cantilever support means carried on and vertically movable along said one mast section, said carriage having cantilever load lifting members extending therefrom for supporting a load with its center of gravity spaced horizontally outwardly from the mast, counterbalancing arm means fixedly mounted on and extending from said mast section in a direction generally opposite to said load lifting members, and flexible tension means adapted to be operably interconnected with said extending mechanism and said mast section for exerting in tension a load lifting force on said carriage in response to actuation of said extending mechanism to cause vertical load lifting movement of saId carriage, support means mounted on said mast section and arm means and training said flexible means thereon such that said flexible means has a first run extending vertically downwardly to a load lifting connection with said carriage and a second run extending vertically downwardly from said arm means at a point spaced horizontally in said opposite direction by a predetermined distance, and connector means for operably connecting said second run to said mast at a support point remote from said assembly at an elevation below said arm means to exert a downward pull via said second run to develop the upward pull in said first run which lifts said carriage, said predetermined distance being correlated with the said load lifting pull in said flexible means such that said second run acting on said arm means develops a moment acting on said mast section proportional to and oppositely to the load induced moment exerted via said carriage and cantilever support means on said mast section so as to substantially counterbalance load induced bending forces acting on said mast section whereby said bending forces are reacted in said mast section to thereby isolate the upper end of the mast from said bending forces.
 9. In a load lifting mechanism for a vehicle the combination comprising an extensible mast including a hydraulic ram and a vertically movable mast section supported by said ram and vertically elevated by actuation of said ram, guide means maintaining said mast section in angular alignment with said ram, load lifting means carried on and vertically movable along said mast section and extending therefrom for supporting a load with its center of gravity spaced horizontally outwardly from said ram, counterbalancing arm means fixedly mounted on and extending from said mast section in the vicinity of the upper end thereof in a direction generally opposite to said load lifting means, and flexible tension means operably interconnecting said ram and mast section for exerting in tension a load lifting force on said load lifting means in response to actuation of said ram to cause vertical load lifting movement of said load lifting means, said flexible means being connected to said counterbalancing arm means and extending downwardly from said arm means at a point spaced horizontally in said opposite direction by a predetermined distance correlated with the tension force in said flexible means such that said flexible means acting on said arm means develops a moment acting on said mast section proportional to and oppositely to the load induced moment exerted via said load lifting means to thereby substantially counterbalance load induced bending forces acting on said mast, said load lifting means including a carriage having means engaged with said mast section for vertically guiding movement of said carriage on said mast section and cantilever load lifting members carried on said carriage and extending therefrom for supporting a load with its center of gravity spaced horizontally outwardly from said ram, said flexible means operably interconnecting said carriage, ram and mast for lifting said carriage on said mast section in response to expansion of said ram, said flexible means being trained over said counterbalancing arm means and having a first run extending downwardly from said arm means to a load lifting connection with said carriage means and a second run extending downwardly from said arm means at said point such that said second run acting on said counterbalancing arm means develops said counterbalancing moment, said extensible mast further including a second mast section adapted to be supported in fixed position near its lower end on the vehicle, said first and second mast sections each having a pair of horizontally spaced upright rails, said counterbalancing arm means comprising a pair of arms individually cantilever connected to the upper ends of said first section rails and extending generally horizontally therefrom in said opposite direction and being spaced from one Another laterally of said mast, said mast further including a pair or orienting arms individually cantilever connected to the upper ends of said second section rails and extending therefrom generally in vertical alignment with said counterbalancing arms, said flexible means comprising a first pair of flexible tension elements disposed one adjacent each side of said mast and each having said first and second runs, first and second rollers rotatably carried on each of said counterbalancing arms respectively supporting said first and second runs of the associated flexible elements vertically above said carriage means and at said point respectively, third and fourth rollers rotatably supported on each of said orienting arms generally vertically aligned with said first and second rollers respectively of the aligned counterbalancing arm, fifth rollers rotatably supported one on each side of one of said ram members near the lower end of said ram, said second runs running vertically downwardly from the associated second rollers to and under the associated third rollers and thence to and over the associated fourth rollers then down and under the associated fifth rollers and thence upwardly to a fixed connection with said fixed mast section.
 10. The combination set forth in claim 9 wherein said ram comprises a cylinder member and a plunger member telescopically received in said cylinder member, and wherein said guide means comprises key and keyway means disposed radially intermediate said ram members and extending axially thereof in sliding engagement with at least one of said ram members to prevent relative rotation therebetween and to provide a slide bearing therebetween.
 11. The combination set forth in claim 10 wherein said guide means also includes a crosshead secured to the upper end of the uppermost of said ram members, said crosshead having means guidably engaging said mast section.
 12. The combination set forth in claim 10 wherein said cylinder member constitutes the lowermost outer part of said ram and said plunger member constitutes the uppermost inner part of said ram.
 13. The combination set forth in claim 12 wherein said ram plunger member has sixth rollers rotatably supported thereon and the upper end thereof and said mast further includes a second pair of flexible tension means individually connected at one end to said rails of said first mast section and running therefrom vertically upwardly to and over the associated sixth rollers and thence downwardly to a connection with said cylinder member.
 14. The combination set forth in claim 13 wherein said first section rails each has an outwardly facing channel and said carriage means comprise first and second pairs of vertically spaced rollers with one pair tracking in each of said channels of said first section rails, and wherein said second section rails each has an inwardly facing channel, said ram having guide rollers carried on said cylinder member and tracking one in each of said channels of said second section rails.
 15. The combination set forth in claim 14 wherein said second mast section has ram guide rollers rotatably supported thereon in rolling engagement with said cylinder member for guiding vertical movement thereof relative to said second mast section.
 16. In an extensible load lifting mast the combination comprising upper and lower vertically overlappable mast sections, a hydraulic ram interposed between said mast sections and including upper and lower relatively movable members, first roller means journalled on said lower ram member, second roller means journalled on said upper ram member, means for guiding vertical movement of said upper mast section relative to said ram and to said lower mast section, load lifting means supported on said upper mast section, first flexible element means connected to said lower mast section and running therefrom under said first roller means then up to a connection with said load lifting means whereby said ram is suspended on said first element means, and second flexible element means connected to said upper mast section and running upwardly over said second roller means and then downwardly to a connection with said lower ram member, said mast sections being vertically separated from one another by extension of said ram, and wherein said guide means comprises anti-rotation means interengaged between said ram and lower mast section and anti-rotation means interengaged between said ram and upper mast section, said load lifting means including cantilevered load carrying means movably mounted on and extending outwardly from one side of said upper mast section, said upper mast section having counterbalancing arm means fixedly secured thereto and extending therefrom in a direction generally opposite to said load carrying means, said first flexible element means being connected to said counterbalancing arm means at a point thereon spaced outwardly from said ram and extending downwardly therefrom to exert a downward force on said arm means at said point proportioned to the load lifting force transmitted via said flexible element means.
 17. A vertically extensible load lifting mast for a lift truck including in combination first, second, third and fourth mast sections each having a pair of horizontally spaced upright rails successively telescopically interengaged for supporting said mast against bending stresses, said first section constituting the lowermost fixed section of said mast adapted for attachment to the lift truck, said fourth section constituting the uppermost section of the mast, a load lifting carriage having roller means tracking in said rails of said fourth section supporting said carriage for vertical movement along the front of said mast, a hydraulic ram disposed between and generally parallel to said rails and comprising an external cylinder and a plunger telescopically received therein and extending from the upper end thereof, a pair of first rollers rotatably mounted on said cylinder near the lower end thereof, a pair of second rollers rotatably mounted on said fourth mast section near the upper end thereof, a first pair of chains each connected at one end thereof to said first mast section and at the other end thereof to said carriage, said chains being trained around said first and second rollers intermediate said ends thereof whereby said ram is suspended on said first chains, a third set of rollers rotatably mounted on said plunger near the upper end thereof, a second pair of chains each connected at one end to said carriage and at the other end to said cylinder and being trained over said third rollers intermediate said ends thereof whereby said fourth mast section is suspended on said second chains, means directly interconnecting said plunger with said third mast section and means directly interconnecting said cylinder with said second mast section.
 18. The combination set forth in claim 7 wherein said connector means comprises a rigid frame connected to said lowermost section of said mast at point spaced vertically above the lower end thereof, said frame being adapted to be connected to said truck at a point spaced from said mast in said opposite direction, said frame extending in said opposite direction a distance greater than the extent of said counterbalance arms and adapted to extend over an operator station on the truck at an elevation adapted to provide operator clearance thereunder and being constructed to serve as an overhead guard therefor.
 19. The load lifting mechanism as set forth in claim 1 wherein said ram comprises a cylinder and a plunger telescopically received in said cylinder, said connector means comprising bracing means mounted on said cylinder and extending generally rearwardly therefrom, said guide means including a crosshead bracket mounted on the upper end of said plunger, second counterbalancing arm means mounted on said crosshead and extending therefrom above and generally in vertical alignment with said bracing means, said mast section being mounted for vertiCally guided movement on said crosshead, said first-mentioned counterbalancing arm means extending from said mast section above and generally in vertical alignment with said second counterbalancing arm means, first roller means mounted on said plunger near the upper end thereof, second roller means mounted on said second counterbalancing arm means spaced from said first roller means, said flexible element means further comprising chain means associated with said second counterbalancing arm means and connected at one end to said mast section and at the other end to said bracing means and being trained intermediate said ends over said roller means, said second run being connected to said second counterbalancing arm means whereby said connector means comprises said bracing means, said chain means and said second arm means.
 20. The combination set forth in claim 19 wherein said second roller means is located between said crosshead and the connection of said second run to said second arm means, said second support means being generally vertically aligned above the connection of said second run to said second arm means.
 21. The combination set forth in claim 20 wherein said mast section has a pair of horizontally spaced upright rails each having a channel facing inwardly toward the channel of the other rail and said ram is disposed between said channels, and wherein said crosshead has a pair of vertically spaced rollers on each side thereof tracking in said channel of the adjacent one of said rails.
 22. The load lifting mechanism as set forth in claim 1 wherein said ram includes a cylinder and a plunger telescopically received therein and extending from the upper end thereof, said mast section being mounted on said plunger for movement therewith, said mast section including a pair of horizontally spaced upright rails each having a channel, said ram being disposed between and extending parallel to said rails, said guide means comprising a pair of guide rollers mounted on said cylinder with one of said rollers tracking in each of said channels, said counterbalancing arm means comprising a pair of counterbalancing arms mounted on said mast section and extending therefrom in said opposite direction, said first and second support means comprising respectively a pair of first rollers mounted on said mast section generally above the path of travel of said carriage and a pair of second rollers individually mounted on said arms spaced from said first rollers, said flexible element means comprising a pair of chains one associated with each of said arms each connected at one end to said carriage and extending upwardly therefrom and thus defining said first run and thence over the associated first roller and thence to the associated second roller and thence downwardly to the other end of said chain and thus defining said second run, said connector means operably connecting the other end of each of said chains in fixed relation to said ram cylinder.
 23. The combination set forth in claim 22 wherein each of said rails of said mast section have an outwardly facing channel, and further including first and second sets of vertically spaced rollers mounted on said carriage and disposed with one set in tracking relation in each of said outwardly facing channels, and wherein said first-mentioned channels constitute inwardly facing channels. 